Benzo[a]pyrene (BP) and 2-amino-1 -methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are widespread procarcinogens to which people are exposed through numerous sources including tobacco smoke, auto emissions, and the diet. Both chemicals are metabolically activated by the cytochrome P4501 family enzymes CYP1A1 and CYP1A2. Recently, Dr. Sutter's group cloned and identified the human cDNA for a novel cytochrome P450 enzyme, CYP1B1, that is induced in response to treatment with 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD) (Sutter et al, 1994). Given that the predicted protein sequence of CYP1B1 is more similar to CYP1A1 and CYP1A2 than any other protein, it is likely that this novel P450 also metabolizes carcinogenic substrates. Similarly, it is likely that CYP1B1 may influence human cancer risk since CYP1A1 and CYP1A2 are implicated in human lung and colon cancer risk. The specific aim of this proposal is to test the hypothesis that the human CYP1B1 protein metabolizes the BP and PHIP. The metabolic profile of human CYP1B1 will be determined using recombinant yeast expressing human CYP1A1 and transformed human cell lines expressing CYP1A1 and/or CYP1B1. Specific metabolites will be identified by high pressure liquid chromatography (HPLC) and synchronous fluorescence spectroscopy (SFS). In addition, a panel of human DNAs will be screened for CYP1B1 polymorphisms. These studies represent the first detailed investigations of human CYP1B1 function.